1. Field of the Invention
The present invention relates to a substrate that can be used for the patterning of nanocrystals, and to a method for forming a pattern of nanocrystals using the substrate. More specifically, the substrate comprises an inorganic layer having a modified surface, wherein the modified surface is formed by coating a surface of the inorganic layer with a bifunctional molecule comprising a functional group having an affinity for a nanocrystal at one end of the molecule, and a functional group having an affinity for the inorganic layer at the other end of the molecule. A method for forming a pattern of nanocrystals using the substrate is also provided.
2. Description of the Related Art
A nanocrystal is a single crystal particle having a cross-section of only a few nanometers. Since a nanocrystal has a large surface area per unit volume, most of the constituent atoms of the nanocrystal are present on the surface of the nanocrystal. As a consequence of this characteristic structure, a nanocrystal exhibits quantum confinement effects and demonstrates electrical, magnetic, optical, chemical and mechanical properties that are substantially different from those inherent to the constituent atoms of the nanocrystal. In particular, semiconductor nanocrystals have high luminescence efficiency and a small half bandwidth within the photoluminescence (“PL”) spectrum, making their use advantageous for application to light-emitting materials. As a result, semiconductor nanocrystals have received a great deal of attention for their potential use as materials for light-emitting layers of various electroluminescent (“EL”) devices and display devices.
For example, a prior art electroluminescent device, as shown in FIG. 1A, may have a structure including a cathode 10, an electron transport layer 20, a nanocrystal light-emitting layer 30, a hole transport layer 40, and an anode 50, that are sequentially stacked on a substrate. Application of the nanocrystals as light-emitting layer materials for various display devices, as shown in FIG. 1B, shows that the nanocrystal light-emitting layer 30 be patterned into nanocrystal patterns that correspond to each red, green and blue (“RGB”) wavelength. Furthermore, with the recent trend toward display devices of reduced size and weight, there is an increased demand for pattern miniaturization.
In an attempt to find techniques for forming a pattern of nanocrystals, studies have been conducted utilizing various methods that include ink-jet printing, a self-assembly method, and the like. However, recently a nanoimprinting lithography (“NIL”) technique has attracted a great deal of interest across a variety of fields, including the semiconductor industry, as a promising ultra-fine patterning technique for use in nano-devices. Nanoimprinting lithography can transfer high-resolution fine patterns on a substrate through a low-cost and simple process, and therefore nanocrystal patterns can be formed in an inexpensive and effective manner.
Nanoimprinting lithography is a convenient method for forming patterns of nanocrystals by preparing a nanocrystal thin film on a patterned stamp and then repeatedly stamping the thus-formed thin film on the desired substrate. For example, according to the nanoimprinting method, patterned nanocrystal thin films can be formed on inorganic layers of inorganic electroluminescent (EL) devices. The nanocrystal thin films patterned according to the nanoimprinting lithography methods can be used for a wide variety of applications including inorganic EL devices, backlight units (BLU), nano-bio devices, and the like.
Research is currently ongoing to develop a method capable of more stably forming a desired pattern for use in nanoimprinting lithography. In this regard, the most important thing is to ensure the efficient transfer of nanocrystals, in a desired pattern, to the substrate. That is, if there is no strong attractive force between the nanocrystal thin film formed on a stamp, and the inorganic layer formed on the substrate, to which the nanocrystal thin film will be applied, the thin film is poorly transferred and remains on the stamp. Consequently, it is impossible to achieve transfer of a uniform nanocrystal pattern onto the substrate. Further, even when the nanocrystal thin film transfers sufficiently onto the substrate, it may be impossible to maintain the original uniform state of the thin film due to the separation of nanocrystals in subsequent post-treatment processes.
In an attempt to solve these problems, a method for modifying the surface of the stamp has been proposed. However, such a surface modification technique is problematic due to the high level of complexity involved.